SNAIL-SHELLS. 213 



by the friction of stones and rocks ; this drift is carried away by 

 the streams, and often deposited at a considerable distance from 

 the glaciers. Masses of yellowish sand and mud produced in 

 this way are to be found in the whole basin of the Rhine, from 

 the Schollberg (Canton of St. Gall) to Hesse and Nassau. In 

 the neighbourhood of Mayence they occur of great thickness. 

 This formation [is termed " fluviatile loam " by Sir Charles 

 Lyell, and] is known under the name of Loess. Here and there 

 it contains great quantities of snail-shells, almost all belonging 

 to living species. In Switzerland such shells were found by 

 Professor A. Escher de la Linth in a Loess formation at the 

 Schollberg (between the Hochwand and Triibbach) and in the 

 bay of Murris, which opens towards the south (below the ruins 

 of the Wartau) in the St. -Gall portion of the Rhine valley. 

 The 21 species * determined by Professor Mousson still, without 

 exception, occur in Eastern Switzerland, most of them in the 

 valley of the Rhine or at the foot of the nearest mountain- slopes. 

 One of the most abundant species (Helix ruderata, Stud.), how- 

 ever, is now wanting in the plain, and is a characteristic form 

 of the high mountain -region, occurring in the mountains of 

 Glaris, the Prattigau, and the Sentis chain. Helix sericea gla- 

 bella, Stud., and H. arbustorum subalpina also belong to the 

 mountain-regions. All the other species are either forest-snails 

 from the region of leafy trees, or species which prefer shady 

 moist places. Inhabitants of dry sunny localities are wanting. 

 These shells probably remain from a time when the glacier 

 had retreated into the neighbourhood of Sargans or Ragatz, and 

 the fine sand and mud were deposited upon the old bed of the 

 glacier. The intermixture of some mountain forms which are 

 no longer to be found in the low country, shows that the glacier 



* See Mousson, " Ueber den Loess des St.-Gallischen Rheinthales ' ' (in 

 Mittheil. der Ziircher naturf. Gesellsch.1856. The species found are : Succinea 

 oblonaa, Drap. ; Helix nitidula, Drap., var. vitrina, Hoch.; H. nitidosa, Fr.; 

 H, nitens, Mich. ; H. crystallina, Mull. ; H. fulva, Drap. j H. ruderata, Stad. ; 

 //. rotundata, Mull. ; //. sericea, Mull., 'glabella and hijbrida ; H. villosa, Drap. ; 

 H. striaella late umbilicata ; //. pulchella costata, obvoluta, Mull. ; //. arbusto- 

 rum subalpina; H. hortensis; BuUmns montanus, Drap.; Achatina lubrica, 

 Miill., with var. pulchella ; Pupa dolium,P. biyranata, P. secale, Clamilia dubia, 

 Drap. It is very remarkable that the variety of Helix striyella \vith a wide 

 umbilicus still occurs near Sargaus, and is peculiar to that district. 



